Solar air conditioning is of two types:
- Continuous air conditioning.
- Intermittent absorption air conditioning.
Further two different refrigerant systems are used in the type of continuous absorption air conditioner:
- Lithium bromide-water system
- Ammonia-water system.
Water is the refrigerant and lithium bromide is the absorbent in the lithium bromide-water system while ammonia is the refrigerant and water is the absorbent in ammonia water system.
The solar air conditioner has five important components namely generator, condenser, evaporator, absorber and heat exchanger.
Continuous air conditioning
- Thermal energy of the hot water in a storage tank is supplied to the refrigerant/absorber pair in the generator and the refrigerant is distilled out.
- The refrigerant is condensed.
- On passing through the pressure reducing valve to the evaporator, the refrigerant cools the space and evaporates.
- The refrigerant vapour is absorbed in the absorber and the refrigerant is ready for the next cooling cycle.
Lithium bromide-water system is more advantageous than the ammonia-water system and relatively studied more. Coefficient of performance (COP) of lithium bromide-water system is more than that of ammonia-water system. The schematic diagram of the solar based absorption air conditioner is shown below:
Intermittent absorption air conditioning
The intermittent absorption air conditioning is operated in tune with the availability of solar radiation. The refrigerant is distilled out of the absorber by the solar heat. The refrigerant is compressed, condensed, expanded through a valve and then evaporates taking up the energy from the space to be cooled and thus completes the cycle. The coefficient of performance (COP) of the system is about 0.60.
Adsorption air conditioning
The adsorption air conditioning involves the removal of gaseous substances from solid by solar heat.
- The vapour is condensed and stored.
- On cooling demand the condensed gas evaporates by absorbing heat from the space to be cooled and the vapour is absorbed in the solid material and the system goes on in cycle.
- The increase in the temperature of the absorbent material induces a pressure increase which could drive the refrigerant out of the molecule.
This is an intermittent system. If one or more air conditioning systems are included, then the system can function continuously. The uptake of the refrigerant by the material such as zeolite and silica are perfectly reversible and hence could be used for the solar refrigeration. The coefficient of performance (COP) of the system is about 0.60.
Solar air cooling is yet to be made commercially viable.
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